Related Field
The present invention relates to a method for additive manufacturing of three-dimensional articles.
Description of Related Art
Freeform fabrication or additive manufacturing is a method for forming three-dimensional articles through successive fusion of chosen parts of powder layers applied to a worktable. A method and apparatus according to this technique is disclosed in US 2009/0152771.
Such an apparatus may comprise a work table on which the three-dimensional article is to be formed, a powder dispenser, arranged to lay down a thin layer of powder on the work table for the formation of a powder bed, a ray gun for delivering energy to the powder whereby fusion of the powder takes place, elements for control of the ray given off by the ray gun over the powder bed for the formation of a cross section of the three-dimensional article through fusion of parts of the powder bed, and a controlling computer, in which information is stored concerning consecutive cross sections of the three-dimensional article. A three-dimensional article is formed through consecutive fusions of consecutively formed cross sections of powder layers, successively laid down by the powder dispenser.
FIGS. 1A(i)-1A(iii) depict a first prior art hatch algorithm for three different layers of a three-dimensional article where the same melt beam current for an entire layer is used. The melt beam current is depending upon the entire layer area. No correction or compensation was made for long or short scan length, leading to vast differences in melt behavior of the two. For example short scan lengths were excessively overmelted, whereas long scan length lacked energy contribution. As a result the microstructure was coarse and heavily swelled on small areas and fine but filled with pores on longer scan length.
FIGS. 1B(i)-1B(ii) depict a second prior art hatch algorithm for three different layers of a three-dimensional article where the energy and scan speed of the energy beam is adjusted depending on the scan length and therefore kept the time in between hatches fairly constant. However, varying the energy and the scan speed will change other parameters such as the solidification rate and thermal gradient which in turn determines the microstructural properties.
There is a demand for additive manufacturing techniques which is capable of building three-dimensional articles with predictable and repeatable material characteristics which is independent of the shape and size of the three dimensional article to be built.